Alloy steel for the manufacture of motor valves



Patented Apr. 2, 1940 PATENT OFFlCE ALLOY STEEL FOR THE MOTOR VALVES George R. Rich, Battle Creek,

Rich Manufacturing Corporation, Mich., a corporation of Michigan Mich, assignor to Battle Creek,

No Drawing. Application February 3, 1940, Serial N; 317,106

'7 Claims.

This invention relates to alloy steel for the manufacture of motor valves and parts of plural piece motor valves.- As is well known, motor valves are operated at very high temperatures, and alloy' steels that are suitable for use in valves operated at room or other relatively low temperatures, are not usable as motor valve steels.

The valves in modern motors designed for increased power and higher speeds must resist the combined action of heat, corrosion, wear, and stresses to a much greater degree than any other part of the engine. The use of doped fuels also adds to the severity of operating conditions to which valves are subjected. In view of these numerous and rigid requirements, relatively few steels are suitable for this purpose. Valve steels used at the present time fall into two general categories: (a) highly alloyed austenitic stainless steels and (1)) medium alloyed pearlitic steels such as the commonly used Silchrome steel.

The motor operating temperature is of paramount importance in the selection of a valve steel. The operating speed and the valve spring pressure, as well as the temperature of opera- 2 tion of a motor are the factors which govern the valve stresses. Up to the present time, it has been found that only highly-alloyed austenitic steels can withstand high-temperature motor conditions and extreme valve stresses. Cooler motors usually employ the relatively cheaper pearlitic type steels such as Silchrome.

Both these classes of steel, however, have certain undesirable characteristics which must be overcome before insured safe and eflicient valve 35 performance may belealized. A very serious objection to the use of austenitic steels for valves is the fact that they wear very poorly along the stem. The stems of such valves score very easily when operating in cast-iron valve guides. Poor wear and scoring often serve to decrease the life of a valve and materially decrease motor efliciency, especially at higher speeds. The low hardness of this material introduces excessive wear and gradual upsetting of the tappet-end of such valves in motors which employ high 45 valve-spring pressures. In addition to these bad I mechanical features of austenitic steel valves,

the extremely high price of this material is an important factor for consideration.

The Silchrome type steels are more economical than austenitic steels, but since they possess relatively low tensile strength at elevated temperatures, they may be used only in cooler motors'. Even in the cooler type of engines, valves 5 of this material have a tendency to become embrittled after exposure to motor operating conditions.

I have produced a new motor valve alloy steel of three dillferentv grades, herein designated as A, B, and C, which I believe satisfies the general requirement for valves and does not possess the bad features of austenitic and Silchrome steels. This new steel is cheaper than either austenitic steels or the Silchrome steels, in fact, the new steel costs about 40% less than austenitic steels and about less than the Silchrome type steels. By careful selection and control of the compositions within very close limits, I have developed one grade of the steel applicable to metors with high operating temperature, a second grade suitable for use in cooler motors, and a third which serves well in motors operating at intermediate temperatures. A chemical analyses of the steel and the types of motors in which each grade of the steel may be used is as follows: Grade A Range Specific Per cent Per cent 0.90 to i. 20 1.00

0. 025 max. 0. 025 max.

0. 025 max. 0. 025 max The remainder The remainder Steel containing the above analysis is for use in valves for motors operating at low tempera-- tures, such as Buick, Pontiac, Nash, and tractors.

Grade B The analysis for this grade is the same as that for Grades A and B, except that the range of chromium content is from 9.25 to 9.75 percent I and the specific amount is 9.50 per cent.

' Steel containing the above analysis is for use in motors operating at high temperatures, such.

as Cadil1ac', Ford, Hercules motors, and trucks.

Valve steels must withstand the oxidizing and corrosive action of the hot exhaust gases of a motor. The addition of anti-knock compounds to present day motor fuels has increased not only the oxidizing characteristics of the exhaust gases, but also has made them extremely corrosive. Laboratory oxidation tests indicate that the present steel has somewhat better oxidation and corrosion resistance characteristics than'Silchrome steel.

The gradual increase in chromium content coupled with the fixed proportions of the other elements in the present steel results in a gradual increase in the oxidation and corrosion resistance.

Hence it is necessary to determine the operating temperature of a particular motor in order to select the most economical of the three grades of steel which will serve most satisfactorily.

Since chromium increases tensile strength at elevated temperatures a high-temperature tensile strength is developed in each grade that satisfies the strength requirements of the class of motor to which it is applicable.

The impact strength, a measure of toughness, of the three grades of the steel, is much higher than that of Silchrome steel. The toughness of Silchrome steel is particularly inferior; it becomes very brittle after prolonged heating and fails very easily when subjected to sudden impact. Valves used in high-temperature motors require greater impact strength than those used in motors operating at low temperatures. The higher chromium content of Grade C of the present steel renders this steel more suitable for hightemperature motors, while the lower chromium contents of Grades A and B are suflicient to meet the impact requirements of valves used in lowtemperature and intermediate-temperature motors, respectively.

Many valve failures may be attributed to a corrosion-fatigue phenomenon, a combined action of fatigue stresses and the oxidizing and corrosive attack of hot exhaust gases. Since the fatigueproperties of steels are similar to their toughness characteristics, it appears that the fatigue limits of the three grades of the steel closely parallel their impact strengths. By virtue of the chromium content of these three grades of the steel, the highest fatigue strength is developed in the steel which is exposed to the most severe fatigue, oxidation, and corrosive conditions.

The present steel, by virtue of its chemical composition, has a greater hardness at room temperature and retains this hardness to a greater degree after heating than other steels. The hardness is, moreover, very uniform throughout the entire valve. Such uniformity will minimize the residual stresses in a valve and for this reason decreases the susceptibility to warping.

The relatively high and uniform hardnessat the valve seat is a distinct advantage for the purpose of eliminating pick-up on this surface. Pick-up on the seat leads to faulty seating and compression loss. If this condition becomes too pronounced, the valves must be reground, otherwise burning of the valve seat will result. Much difliculty is encountered in this regard with aijstsnttic steels which are inherently soft. The va s made of the present steel show a remarkably small tendency for pick-up" even under most severe motor operating conditions. In spite of this relatively high hardness, th present steel can be machined readily on a production basis.

A motor valve must be capable ofbeing heated to the maximum temperature which it may attain in a motor and yet retain its properties at that temperature for a long period of time. In order to meet this requirement, the critical temperature should be as high as possible, so that the difference between the critical and the motor operating temperature is a maximum. The critical of Grade. A steel is approximately 1600 F.; the increased chromium contents of Grades B and C will raise their criticals to still higher temperatures. Motor tests have shown that the critical temperature of each of the three grades is sufficiently high to insure the necessary strength and toughness required at the operating temperatures of each of the three classes of motors even after prolonged exposure to these temperatures.

The present steel lends itself very nicely to the modern production forging practices. It has been found that this steel must be forged within a very close temperature range, between l850 and 1900 F. For best results the steel must be heated evenly and uniformly.

ened-by burn-hardening" and withstanding the,

continuous pounding of tappets very effectively. Heat treating in this manner develops in the finished valve the best combination of strength, toughness and ductility, a relatively hard but easily machinable structure capable of being ground 'to a very fine finish which has exceptional wearing qualities.

In addition to high strength and oxidation resistance, the present developed steel is free from temper embrittlement which may be defined as the loss in ductility and impact strengths of a steel at room temperature after prolonged heating at some elevated temperature. This defect, common to some valve steels, has been remedied through the use of approximately 0.60% molybdenum in the composition.

Among the advantages of the present alloy steel are its superior physical and chemical properties; its resistance to temperembrittlement, and its tensile strength are superior to any known high chrome steels; it was the brittleness developed in high chrome steels which caused automotive engineers to discontinue their use and substitute other types of valve steels.

Tests for tensile strength of the material have shown that the tensile strength of the material is far above that of the known valve steels. For instance, when heated to 1300 F. the material shows a tensile strength of 27,500 pounds per square inch, with an accompanying reduction in area of 45.8%,as against 18,300 pounds in one of the best known valve steels. At 1400" F. it showed a tensile strength of 17,500 pounds and at 1560 IF. it showed a tensile strength of 12,600 pounds. These figures are far above the tensile strength of other well known valve steels.

Tests for acid resisting properties as compared with those of well known valve steels, have demonstrated thatthe acid resistance of the present steel is far above that of well-known valve steel. When tested in a bath of 4% sulphuric acid at various predetermined temperatures for various lengths of time, the resistance of the steel was computed and it was found that its acid resistance was greater by 3% to 42% than that of well known valve steels.

These important characteristics of the present alloy steel is due, it is believed, to the particular alloys used in and about the proportions specified.

I claim as new and desire to secure-by Letters Patent:

1. An alloy steel for the manufacture of motor valves and parts thereof capable of continued efiicient use at elevated temperatures, composed of carbon 0.27 to 0.32 per cent; chromium 7.25 to 9.50 per cent; silicon, 3.10 to 3.40 per cent; nickel, 1.90 to 2.20 per cent; manganese, 0.90 to 1.20 per cent; molybdenum, 0.50 to 0.75 per cent;

phosphorus 0.025 per cent, maximum; sulphur,

0.025 per cent, maximum, and the remainder iron.

2. An alloy steel for the manufacture of motor valves and parts thereof capable of continued efficient use at elevated temperatures, composed of carbon 0.27 to 0.32 per cent; chromium, 7.25 to 7.75 per cent; silicon, 3.10 to 3A0 per cent; nickel, 1.90 to 2.20 per cent; manganese, 0.90 to 1.20 per cent; molybdenum, 0.50 to 0.75 per cent; phosphorus 0.025 per cent, maximum; sulphur, 0.025 per cent, maximum; and the remainder 3. An alloy steel for the manufacture of motor valves and parts thereof capable of continued efiicient use at elevated temperatures, composed of carbon, 0.25 to 0.32 per cent; chromium, 8.25 to 8.75 per cent; silicon, 3.10 to 3.40 per cent; nickel, 1.90 to 2.20 per cent; manganese, 0.90 to 1.20 per cent; molybdenum, 0.50 to 0.75 per cent; phosphorus 0.025 percent, maximum; sulphur, 0.025 per cent, maximum; and the remainder iron.

4. An alloy steel for the manufacture of motor valves and parts thereof capable of continued eflicient use at elevated temperatures, composed of carbon, 0.25 to 0.32 per cent; chromium, 7.50 per cent; silicon, 3.10 to 3.40 per cent; nickel, 1.90 to 2.20 per cent; manganese, 0.90 to 1.20 per cent; molybdenum, 0.50 to 0.75 per cent; phosphorus, 0.025 per cent, maximum; sulphur, 0.025 per cent, maximum, and the remainder iron.

5. An alloy steel for the manufacture of motor valves and parts thereof capable of continued efficient use at elevated temperatures, composed of carbon, 0.25 to 0.32 per cent; chromium, 8.50 per cent; silicon, 3.10 to 3.40 per cent; nickel, 1.90 to 2.20 per cent; manganese, 0.90 to 1.20 per cent; molybdenum, 0.50 to 0.75 per cent; phosphorus, 0.025 per cent, maximum; sulphur, 0.025 per cent, maximum; and the remainder iron.

6. An alloy steel for the manufacture of motor valves and parts thereof capable of continued emcient use at elevatedtemperatures, composed of carbon 0.25 to 0.32 per cent; chromium, 9.25 to 9.75 per cent; 'si1icon, 3.10 to 3.40 per cent; nickel, 1.90 to 2.20 per cent; manganese, 0.90 to 1.20 per cent; molybdenum, 0.50 to 0.75 per cent; phosphorus, 0.025 per cent, maximum; sulphur, 0.025 per cent, maximum; and the remainder iron.

7. An alloy steel for the manufacture of motor valves and parts thereof capable of continued emcient use at, elevated temperatures, composed of carbon 0.27 to 0.32 per cent; chromium, 9.50 per cent; silicon, 3.10 to 3.40 per cent; nickel, 1.90 to 2.20 per cent; manganese, 0.90 to 1.20 per cent; molybdenum, 0.50 to 0.75 per cent; phosphorus, 0.025 per cent, maximum; sulphur, 0.025 percent, maximum; and the remainder iron.

GEORGE R. RICH. 

